The present invention relates to an electrophotographic recording apparatus which forms a multicolor image on a surfac e of a photoconductive drum and then transfers the multicolor image to recording paper.
A conventional electrophotographic recording apparatus includes a photoconductive drum around which a corona charger, a first exposure unit, a first developing unit, a second exposure unit, a second developing unit and a transfer unit are disposed, as disclosed in U.S. Pat. No. 4,572,651. In operation, the surface of the photoconductive drum is first uniformly charged by the corona charger and then exposed by the first exposure unit to form a first electrostatic latent image. The first electrostatic latent image is developed with a toner of a first color by the first developing unit. Thus, a first visible image of the first color is formed on the surface of the photoconductive drum. Next, the surface of the photoconductive drum is exposed by the second exposure unit to form a second electrostatic latent image which is then developed by the second developing unit with a toner of a second color different from the first color to form a second visible image. Thus, both the first and second visible images of the first and second colors are formed on the photoconductive drum surface and are simultaneously transferred to a recording paper web by the transfer unit.
In order to prevent the first visible image from being scratched off from the surface of the photoconductive drum by the second developing unit, the first developing unit enables the toner of the first color to have a larger electric charge than the toner of the second color in the second developing unit so that the first visible image strongly adheres to the surface of the photoconductive drum.
In the conventional apparatus, however, the toner of the second color is apt to adhere to the surface of the second, as well as the first electrostatic latent image, which should be developed only with the toner of the first color, because of the remaining electrostatic force of the first latent image. Accordingly, the first visible image of the first color is mixed with the second color, thus impairing the production of a clear first visible image.